1,721,211 research outputs found
Foundations of database systems : an introductory tutorial
No full textA very short overview is given of the principles of databases. The entity relationship model is used to define the conceptual base. Furthermore file management, the hierarchical model, the network model, the relational model and the object oriented model are discussed During the second world war, computers were used for encoding and decoding messages of the English and German army. Only after the war the computers were used for more reasonable and economical reasons. In the beginning of the fifties problems with typically a small amount of input data but for which complex calculations have to be made, were solved using computers. This was due to the small amount of memory and the long access time that was needed. Typical programming languages for this kind of problems emerged: Fortran, Algol and later on Pascal, C and C++. These languages however, were not user friendly enough, nor were they designed to handle huge amounts of complex data. So in the fifties we switched from simple file management to the use of a data structure that was more complex, but that enabled us to solve problems and answer questions that needed a huge quantity of data. We will first introduce the concept of a database and then we will look to a number of
different kinds of databases that have been used from 1960 until now
GOAL : a graph-based object and association language
No full textA graph-based model for describing Schemes and instances of object databases together with a graphical data manipulation language based on pattern matching are introduced. The data model allows the explicit modeling of classes and relations which contain objects and associations, respectively. GOAL consists mainly of two operations, the addition and the deletion. These perform on every part. of the instance where a certain pattern is found. We will present. the syntax and the semantics of the language, and show its computational Completeness
Merging graph-based and Rule-based Computation: the language g-log
No full textIn this paper we discuss the merging of two different computation paradigms: the fixpoint computation for deductive databases and the pattern-matching computation for graph-based languages. We show how these paradigms can be combined on the example of the declarative, graph-based, database query language G-Log. A naive algorithm to compute G-Log programs turns out to be very inefficient. However, we also present a backtracking fixpoint algorithm for Generative G-Log, a syntactical sublanguage of G-Log that, like G-Log, is non-deterministic complete. This algorithm is considerably more efficient, and reduces to the standard fixpoint computation for a sublanguage of Generative G-Log that is a graphical equivalent of Datalog. The paper also studies some interesting properties like satisfiability and triviality, that are undecidable for full G-Log and turn out to be decidable for sufficiently general classes of Generative G-Log programs
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